Author Topic: Temp, Humidity, Density Altitude, Tuners  (Read 6243 times)

Offline rpollock

  • Long Term Resident of BR Addiction Center
  • Administrator
  • Hero Member
  • *****
  • Posts: 1163
  • Country: ca
    • View Profile
Temp, Humidity, Density Altitude, Tuners
« on: March 27, 2010, 02:09:20 PM »
Has anybody else read this thread on the above topic? http://benchrest.com/forums/showthread.php?t=68145 It is time consuming but has a few good bits in there, more towards the end of the thread.

It has a lot of info on tuners and how it relates to tracking temperature and density altitude.

The question is, have any of you bothered to track density altitude? For example, at Rosebud our density altitude in the summer would be about 7000', whereas in Tacoma, WA it would be more like 1000' or less. According to the people in the thread that would really throw the tune out the window. Over the course of a day you could easily see the DA vary 1000-2000' from a cold morning to a hot afternoon

Has anybody taken the steps to track this and deal with it according to previously recorded DA readings and powder measure settings?

Another good tidbit in there is that nodes for the 6PPC are about 1.2 gr apart, according to Beggs. Could it be so simple to move up or down .6gr to get a rifle in tune, when you know it is for sure out of tune?

And you thought you had nothing to think about this weekend!


Offline gyeomans

  • Full Member
  • ***
  • Posts: 76
    • View Profile
Re: Temp, Humidity, Density Altitude, Tuners
« Reply #1 on: March 27, 2010, 03:45:50 PM »
I read another similar post a few yrs ago and started to record and measure DA when shooting groups.  Then my DA meter quit and I got real busy running shoots, business, family, etc and sort of forgot about it.  I still measure temp and humidity when I shoot. 

We don't shoot straight groups so the data is kind of hard to correlate with groups/tune and I really only shoot 1-2 times/month.  Our range in CR is about 1000' with the temp and humidity fairly constant.  Temp varies from -4'C to 8'C in the winter with 60-90% humidity.  Spring  & fall we get 6'C to 20'C with humidity about the same.  The one relay that we shoot 100yd groups, the group sizes are fairly consistant thoughout the year.  Then again none of us are really that good and shoot enough groups on a day to day basis to track.  Most of our shooters don't care either. 

Like I said before, I don't shoot enough groups with one gun to correlate the data.  Sometimes having too many guns is a problem.  Don't tell my wife I said that.

I went to a BR Turkey Shoot in Rock Creek, BC a few yrs ago and worked up a load there for a custom ppc and a 22-250 that I was shooting on the coast.  Rock Creek is 2010' elevation and was -5'C.  DA was 0.  In CR at 1000' and 0'C DA is approx -700.  I had to go up 1 gr of H322 in the ppc to get it to shoot and didn't change the load for the Factory Savage 22-250 at all.  Kinda inconclusive.  I do think old Beggs is right though.  DA has got to effect tune.

Another link with a handy chart.   http://en.wikipedia.org/wiki/Density_altitude 

To answer your question  "have any of you bothered to track density altitude?" Rick, I started to but fell off the wagon

cheers
Greg


Offline Tony Gauthier

  • Hero Member
  • *****
  • Posts: 168
    • View Profile
    • APRA
Re: Temp, Humidity, Density Altitude, Tuners
« Reply #2 on: March 28, 2010, 07:49:39 PM »
I read that and I think Beggs is right about the 1.2 between nodes. Yet I shoot the same load at Tacoma as here. Not that I have ever shot that well in Tacoma in a match, but testing for a couple of days before the match showed the tune to be perfect, so go figure!

Offline rpollock

  • Long Term Resident of BR Addiction Center
  • Administrator
  • Hero Member
  • *****
  • Posts: 1163
  • Country: ca
    • View Profile
Re: Temp, Humidity, Density Altitude, Tuners
« Reply #3 on: March 28, 2010, 08:25:30 PM »
I read that and I think Beggs is right about the 1.2 between nodes. Yet I shoot the same load at Tacoma as here. Not that I have ever shot that well in Tacoma in a match, but testing for a couple of days before the match showed the tune to be perfect, so go figure!

He also says the node repeats every 2000' of density altitude. Rosebud and Tacoma are about 6000' apart in density altitude. In "theory" tuning at Rosebud should still put you on a node in Tacoma.... Seems too easy to me....

Offline cyanchycki

  • Hero Member
  • *****
  • Posts: 842
    • View Profile
    • Selkirk Game and Fish
Re: Temp, Humidity, Density Altitude, Tuners
« Reply #4 on: March 28, 2010, 08:29:34 PM »
Rick how did you find the approximate DA for Rosebud?  There a way to calculate it?

How about tuners, anybody out here trying one or planning on trying one?  I think I will order one from Begg's and give it a try somewhere along the way on my new rifle.....
« Last Edit: March 28, 2010, 08:35:37 PM by cyanchycki »
My house is protected by the good Lord and a GUN............
When I Die I don't wanna go Sober..................................

Offline rpollock

  • Long Term Resident of BR Addiction Center
  • Administrator
  • Hero Member
  • *****
  • Posts: 1163
  • Country: ca
    • View Profile
Re: Temp, Humidity, Density Altitude, Tuners
« Reply #5 on: March 28, 2010, 08:47:51 PM »
There are quite a few online DA calculators.  Here are a couple:
http://wahiduddin.net/calc/calc_da.htm
http://www.csgnetwork.com/densaltcalc.html
You can install a DA calculator app into your Iphone. $1!

Most of the info you need is on weathernetwork.ca and as far as altitude, google earth can get you that. Or look up the nearest airport on google. Close enough for our needs.

I just went by memory that Rosebud is at about 5500' elevation and Tacoma can't be more than 500' elevation. Plug in 25C temp and the density altitudes go way up.

Depending on which calculator you use, you will need local atmospheric pressure, or you will need what is called pressure altitude (what an aircraft altimeter reads when set to 29.92 " of mercury at that location). Local barometric pressure is easier to get!

For sure temp and physical local elevation are the biggest factors, then air pressure, then humidity.

Interesting stuff, but maybe not all that significant? Temp is the big player, but when you travel as much as many have planned this year, it might be nice to know where you sit in terms of DA. One more thing to note in your log book. I plan to keep an eye on DA as the day progresses. For this year it will be more out of curiosity.

Rick

 

SMF spam blocked by CleanTalk